In a statement, Santiago said she filed a resolution calling for a Senate investigation of recent LTFRB rulings that she said further caused traffic gridlocks in major thoroughfares.

"I'm calling for a Senate investigation on these LTFRB issuances because they prejudice public transport safety to benefit only a few. It seems that these issuances violate the Aquino administration's policies for economic development," Santiago said.

The senator particularly singled out Memorandum Circular Numbers 2014-009, which suspended operations against colorum buses and out-of-line operations; and 2014-010, which allowed public utility buses (PUBs) to modify their routes and pass through major thoroughfares, such as EDSA, from 19 June 2014 to 17 October 2014.

She said the suspension of operations against the out-of-line buses "would only legalize and spur the proliferation of unauthorized vehicles, which is inimical to the country’s economic development."

Santiago said legalizing out-of-line routes violate existing laws on land transportation. It also defeats the purpose of the establishment of the Integrated Transport System to decongest traffic in Metro Manila, she added.

The lawmaker also slammed LTFRB’s Board Resolution No. 5, which extended the “No Apprehension Policy” of trucks-for-hire (TH) freight services with green plates from 29 July to 29 August.

She said this also caused more traffic congestion across the metropolis.

"LTFRB's logic escapes me. Allowing these trucks to ply our roads when they are still securing the necessary paperwork in the name of trade and commerce is a flimsy excuse. This is LTFRB failing in their basic regulatory functions," she said.

Santiago alleged LTFRB only consulted the business sector and the trucking companies and not the motorists and commuters about the circulars.

She also cited studies that the LTFRB's "no apprehension policy" increased travel time and decreased travel speed in both lanes in the Commonwealth Ave.-South Superhighway route.

In the southbound lane, the route’s travel time suffered a 73.6 percent increase, while the travel speed slowed to down 41 percent.

The studies also found that, compared with data from June 2013, the LTFRB's "no apprehension policy" increased truck volume in Katipunan Avenue by 80.67 percent, C5-Bagong Ilog by 60.52 percent, and C5-McKinley Hills by 33.07 percent.

The LTFRB rules have also been questioned by the Metro Manila Development Authority.